There are many patents describing polyamide-based multilayer tubes. It is necessary to use multilayers because no polymer or polymerblend exists that has at the same time all the properties of mechanical resistance and resistance to the products transported. However, in most multilayer structures it is necessary to have adhesive layers in order to join the various polymer layers together, which polymer layers are often incompatible, thereby increasing the number of layers and complicating the manufacture.
A tube has now been found that comprises, in succession, an outer layer made of PA-11 (or PA-12), an intermediate layer made of a temperature-resistant polyamide (of the PA-6,10 type) and an inner layer made of conductive or non-conductive PA-11 or PA-12.
The PA-11 (or PA-12) outer layer provides chemical resistance, zinc chloride resistance, impact strength and dynamic properties. The intermediate layer provides the mechanical strength and most particularly the high-temperature pressure resistance. The conductive or non-conductive PA-11 or PA-12 inner layer possibly provides conductivity, mechanical properties and chemical resistance. The layers adhere to one another without a coextrusion tie. The tube may be smooth or ringed or compromise smooth parts and ringed parts. According to other embodiments, the tube may have only two layers.